The TV gives an error, while showing a picture - why?

Question

Cables and wires

I decided to connect my computer to the TV via VGA - HDMI was occupied by the Xbox 360. The first cable refused to show the picture. The second had ripples. (the frequency is not the same, naaernoe) I connected it with the first one again - the TV shows my desktop and says: "Check the signal cable."
I heard on the Internet that Samsung (TV model) needs some kind of additional pin on VGA - they determine the image by it. How to restore vision to the TV and let it see - here it is, my computer?
Operating system - elementary OS 3.1 (who does not know - this is Ubuntu 14.04 with a beautiful desktop)